When using a pouring cup to supply molten metal for investment, sand or other casting, especially in air melt, non-aspirated foundry applications, problems may arise due to build-up of pressure in the mold as the mold atmosphere is trapped by the incoming metal. The mold cavity has limited permeability and the mold atmosphere is unable to readily escape during the pouring operation.
If the system fails to allow the release of the entrapped mold atmosphere during casting, then pressure builds up in the system slowing the rate of fill of the casting cavity. In the most severe cases, the casting will not fill completely resulting in a misfill and rejection. In lesser cases, the fill time is slowed which may result in casting defects, such as folds, or poor fill in areas of fine detail or in thin sections. Clearly, this is a serious problem which may cause costly rework or even total rejection.
The reduction in flow rate by this pressure build-up is exacerbated when a choke, i.e. a restricted flow are such as a filter, is present in the system which will cause the formation of a metallostatic head and a non-aspirated pouring condition. A molten metal filter, such as the well known ceramic foam filters described in U.S. Pat. No. 3,962,081, offers significant advantages in the removal of particulate from the molten metal so that elimination thereof is not a satisfactory solution.
It is, therefore, a principal object of the present invention to provide an apparatus for casting molten metal which eliminates the problem of pressure build-up in the mold as the mold atmosphere is trapped by the incoming metal.
It is a further object of the present invention to provide an apparatus as aforesaid which operates effectively when a choke is present in the system.
It is a further object of the present invention to provide an apparatus as aforesaid which is simple, convenient and expeditious to use on a commercial scale.
Further objects and advantages of the present invention will appear hereinbelow.